About external radiotherapy

External radiotherapy uses high energy X-ray beams, cobalt irradiation or particle beams, such as protons or electrons. The beams are directed at the cancer from a machine outside the body. The most common types of external radiotherapy use photon beams (either as x-rays or gamma rays). The radiotherapy beams destroy the cancer cells in the treatment area. The treatment works by damaging the DNA within the cancer cells. DNA is the genetic code that controls how the body's cells behave. The radiotherapy either damages the DNA directly or creates charged particles called free radicals that damage the DNA.

Cancer cells stop growing or die when their DNA is damaged. When the cells die they are broken down and got rid of by the body. Normal cells in the radiotherapy area may also be damaged but they can usually repair themselves.

External radiotherapy is normally given as a series of short treatment sessions known as fractions. You have it in the radiotherapy department from equipment similar to a large x-ray machine.  Radiotherapy machines vary slightly in how they look and how they work. Many types of external beam radiotherapy are given using a linear accelerator machine (LINAC) which uses electricity to create the radiotherapy beams.

Your doctor chooses the type of radiotherapy and the machine for your treatment according to the type of cancer you have and its position in the body. The machine itself does not touch you and you don’t feel any pain during the treatment. But you may get some discomfort or pain later on from side effects of radiotherapy. This is usually temporary and most side effects can be very well controlled with medicines.

Conformal radiotherapy is a common type of external beam radiotherapy. It is also called 3D conformal radiotherapy (3D CRT). Conformal radiotherapy uses the same types of radiotherapy machine as standard beam external radiotherapy. But the radiotherapists put metal blocks in the path of the radiation beam. The blocks change the shape of the beam so that it ‘conforms’ more closely to the shape of the tumour. Conformal radiotherapy can give a better chance of killing the cancer by giving a higher dose of radiation straight to it. It also means less healthy tissue is included in the radiotherapy field so there are likely to be fewer long term side effects.

Planning conformal radiotherapy is done in three dimensions (3D) - width, height and depth - using CT scanning or an MRI scan.

Conformal radiotherapy is most useful for tumours that are close to important organs and structures in your body. This is because it helps to avoid radiation damage to healthy body tissues and organs. It is used for some prostate cancers and can lower the number of men who have long term side effects of straining and bleeding from the back passage (proctitis) after treatment. It is also used for cancers of the food pipe (oesophageal cancer), some types of lung cancer, bladder cancer, pancreatic cancer, liver cancer, head and neck cancers and brain tumours.

At the moment most radiotherapy departments use conformal radiotherapy. But your doctor may not suggest using conformal radiotherapy unless they think it will be better than standard radiotherapy for your particular type of cancer.

Intensity modulated radiation therapy (IMRT) uses hundreds of tiny devices called collimators to shape the radiotherapy area. The collimators also vary the intensity of the beams during each dose of treatment. The radiotherapy beams are aimed at the tumour from different directions. The collimators can move during treatment so that the machine gives very precise doses to a cancer or to specific areas within the tumour. IMRT focuses a higher radiation dose on the tumour but gives a much smaller dose to surrounding normal tissues than standard radiotherapy. So, side effects may be lower than with standard radiotherapy treatment. Treatment is carefully planned using 3D CT scan images of the patient together with computerised dose calculations to find the dose intensity pattern that best matches the tumour shape.

Currently IMRT is being used to treat some cancers of the prostate, head and neck, breast, thyroid and lung, as well as some women's cancers, liver tumours, brain tumours, lymphomas, children's cancers and sarcomas.

In image guided radiotherapy (IGRT) CT, MRI, or PET scans are taken regularly during the treatment. The scans are processed by computers to show changes in the size and position of the tumour. Your doctors can then change your position during treatment or adjust the radiotherapy dose as needed. This treatment targets the radiation very accurately at the tumour and can reduce the dose to normal healthy tissues. This type of treatment can work well for tumours in areas of the body that may move during treatment, for example due to breathing. CancerHelp UK has a page about image guided radiotherapy.

Tomotherapy is a new type of image guided intensity modulated radiotherapy. A tomotherapy machine combines a CT scanner and an external beam radiotherapy machine. Part of the tomotherapy machine can rotate completely around the patient to take CT scans and give radiotherapy to a very localised area. The machine takes pictures of the tumour just before each treatment session to allow the doctors to target the treatment very precisely. This may reduce the damage to normal body tissues in the area. The treatment is also called helical tomotherapy.

Stereotactic radiotherapy gives radiotherapy in fewer sessions, using smaller radiation fields and higher doses than 3D conformal radiotherapy. A single treatment of this type is sometimes called radiosurgery, Gamma Knife or Cyberknife.

You can have this type of treatment using the usual type of radiotherapy machine, the linear accelerator, which has been specially adapted.  A small linear accelerator machine is mounted on a robotic arm next to the radiotherapy couch. The couch can also change position. This way of giving radiotherapy allows beams to be directed from more angles than standard radiotherapy and so the treatment can target the tumour very precisely. Each of the individual beams gives a small dose of radiotherapy.  Because all the beams meet at the tumour, the cancer gets the full dose.  The radiotherapy specialists plan the treatment so that each beam is aimed very precisely.  This allows them to give a high dose of radiation to the tumour but a much lower dose to the surrounding normal tissues. This also explains why you can have a smaller number of treatments than conventional radiotherapy.

The several different terms people use for the same type of treatment can be very confusing.  You may hear your doctor talk about Cyberknife, Gamma Knife or radiosurgery.  These are really the same thing. Stereotactic radiosurgery is the same as stereotactic radiotherapy, but you usually only have a single treatment rather than several. You still have the treatment from many different angles, all precisely targeted at the tumour.  And because of the precise targeting, you can still have a single high dose treatment without harming surrounding normal tissues.  Cyberknife and Gamma Knife are brand names of machines used to give this type of treatment. But they are only a brand name for the machinery, not the type of treatment itself. And sometimes people use the terms radiosurgery or Cyberknife when you have more than one treatment so you can't always assume that radiosurgery means only one treatment.

Doctors use stereotactic radiotherapy for small, well defined tumours that are deep within the body and likely to move, for example due to breathing. They most commonly use it for tumours in the lung, liver or pancreas, and for some types of brain tumour.

Doctors use stereotactic radiosurgery (or Gamma Knife) for small tumours with well defined edges, mostly brain tumours, such as acoustic neuromas, pituitary adenomas, haemangioblastomas or secondary brain tumours. They also use it for spinal cord tumours. During treatment for a brain tumour your head is held still by a head frame.

You can find detailed information about stereotactic radiotherapy in the brain tumour radiotherapy section of CancerHelp UK. We also have a page explaining Cyberknife treatment in our question and answer section.

One of the newer ways of giving radiotherapy uses a different type of radiation beam called a proton beam. Protons collect energy as they slow down and travel through the body. They then release this energy at their target point – the tumour. This means they can give a higher dose of radiation straight to the cancer, but only to a very small area around it. So there is less chance of damage to nearby healthy tissue. Proton beam radiotherapy machines in the UK are only able to treat cancer of the eye. The machines are not able to treat cancers deeper in the body. Some countries in Europe and the USA are testing and using proton beam radiation for deeper cancers, including a type of spinal cord tumour called chordoma. If proton treatment is suitable for you the NHS pays to send you for treatment abroad – usually to Switzerland or France, but sometimes to the USA. Cancerhelp UK has information about chordoma and proton beam treatment.

Electron beams cannot travel very far through body tissue. This type of radiotherapy is used to treat skin cancers or tumours very close to the surface of the body.

When deciding on your course of treatment your radiotherapist takes into account

• Your type of cancer
• Where your cancer is
• Any previous, current or planned treatment
• Your general health and fitness

This means that your treatment will be individual to you.

A course of radiotherapy treatment aimed at curing cancer usually lasts between 1 to 6 weeks but may be longer than this. Your radiotherapist will tell you how long your treatment will take.

Many patients have daily treatment from Monday to Friday, with a rest at weekends. Others have different treatment plans, such as 3 days a week or treatment twice a day. The radiotherapy staff try to give you an appointment for the same time each day. This gives your body a chance to recover from any side effects between treatments. It also means you can get into a daily routine.

External radiotherapy doesn't make you radioactive. It is safe to be with other people, including children, throughout your treatment.

People react to radiotherapy in different ways

• Some carry on working and just take time off for their treatment
• Others feel tired and want to stay at home
• Some are admitted to hospital

Your doctors and nurses will advise you about how best to manage your course of treatment. If you have a family to look after you may need extra help. Don't be afraid to ask for help from your employer, family or friends, or the staff in the radiotherapy department. As your treatment goes on you'll have more idea of how it makes you feel, so you can make any changes to your daily life.

To reduce the side effects, the full dose of radiation is usually divided into many smaller doses. You have the small doses as a series of treatment sessions called 'fractions'. The fractions add up to a full course of treatment. Palliative radiotherapy to relieve symptoms such as pain is often given in fewer fractions than curative radiotherapy, or even as just one treatment. The radiotherapy dose with each fraction is bigger but fewer fractions are given so the overall dose is lower. So palliative radiotherapy has fewer side effects than curative radiotherapy.